[SE-0104] Protocol-oriented integers (revision 2) (#418)
[SE-0104] Protocol-oriented integers (revision 2) (#418)

* Integer => BinaryInteger

* Remove commented out parts

* Add note for FloatingPoint : SignedArithmetic

* Integer.AbsoluteValue => Arithmetic.Magnitude

* signBitIndex => minimumSignedRepresentationBitWidth

* popcount and leadingZeros

* nthWord => word(at:)

* adding 'bitwise' prefix

* static doubleWidthMultiply and doubleWidthDivide

* replacing rhs with other where appropriate

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